Doing the Reichenbach Falls as part of the Sherlock series? I love it. The idea is so self-indulgent, such a shameless bit of emotional cheating, that I can’t decide whether to stand up and salute or get behind it and shove. The original story being called The Final Problem makes it even easier to crowbar Georges Gusdorf in: “No trick of presentation, even when assisted by genius, can prevent the narrator from always knowing the outcome of the story he tells – he commences…with the problem already solved.” For The Reichenbach Fall, of course, not only does the narrator know how this ultimately turns out (which Doyle didn’t when he wrote The Final Problem) but the story knows it and the audience knows it. The situation offers enormous possibilities for either sleight-of-hand or massively sentimental wallowing, as we all watch John’s emotional breakdown knowing that it will all be fine. (Maybe Sherlock’s final graveyard appearance is an admission that there’s no point trying to play this one for suspense, it’s a tearjerker and isn’t pretending otherwise.)

We start with a self-consciously stylish piece of choreography as Jim Moriaty breaks simultaneously into the Bank of England, Pentonville Prison and the case in which the Crown Jewels are kept, using a smartphone. Well, the latter involves a diamond, some chewing gum and a fire extinguisher, which is pretty good fun in low-tech heisty way. Now, this is the premise of the episode. What it asks us to accept in order for the story to get going. So it seems unreasonable to carp. But am I the only one who feels that if you can use a mobile phone to break into three of the most secure places in Britain in the first five minutes, then we should probably all pack up and go home?

Of course it turns out that this was just a stunt by Cheeky Jim, that he wanted to get clapped in jail so the next stage of his evil scheme could begin. (Thus making this sequence a show-off version of the bank robbery at the beginning of Prison Break, minus the tattoos and the plot-essential topless structural engineering.) But I did get a vague feeling that this opening was slightly sawing through the branch it sat on: if we are intended to engage with the mechanics of crime fiction which this show deploys, it might help if that whole edifice wasn’t rendered a bit obsolete by a few keystrokes from a magic handy at the beginning. I was, however, looking at all this from the wrong angle, according to a friend. Gatiss and Moffat, she explained, are science-fiction writers who can’t really script technology. Hence the whiff of the sonic screwdriver about the MacGuffin at the centre of this episode: a computer code which can bypass all security systems. It just can. No, don’t try to work it out. Stop thinking about it right now. Onto the next paragraph, quickly please.

Before escaping his trial via a little heavy-handed witness intimidation, Moraity has convinced the criminal underworld that Sherlock has the code and framed Sherlock for the kidnapping of the British ambassador’s children. Still no longer content, he proceeds to manufacture a false identity for himself as a journalist who helped Sherlock fake all his cases. Thus the detective finds himself on the run from a series of international assassins (who turn out to be protecting him under Mycroft’s orders, and thus probably find all this running a bit unnecessary), the police who believe he has spent the last few years on a combined crime spree/ spoiler binge, and the press who are shocked, shocked I tell you, at the news than a journalist would assist anyone in making things up which were not in fact the case. It all comes together on the top of a building, and Sherlock is offered a choice: everyone he loves dies, or they live on believing he was a murderous fraud.

With this episode we’ve clearly reached “high concept” territory. The plot has shrugged off any expectations that it will make sense, or could be followed analytically. Which is rather a good thing, since it frees up the audience to listen to what the episode is actually saying. Listening to Sherlock is an odd and enjoyable experience, since the show doesn’t so much have a subtext, or indeed a text, as surtitles. Every now and then someone will scream The Point Of It All at you – which I suppose is necessary when you’ve cast the inscrutable, or simply illegible, Cumberbatch in the main role. It’s like watching a silent movie where everyone dashes around excitably and then a card flashes up informing you that “She Surrendered All For Love” or “The House of Stuart has fallen”. Either that, or it’s like playing a game of incompetent and increasingly irritable charades, where someone cracks after fifteen minutes of baffling mime and yells the answer: “Paradise Lost, for sod’s sake! Are you all utterly moronic? Paradise Lost!”

The first few times it happens you cringe, as someone points out helpfully that OTHER PEOPLE SEEM TO HAVE EMOTIONS, BUT SHERLOCK DOESN’T, or JOHN AND SHERLOCK ARE SORT OF LIKE A COUPLE, HAVE YOU NOTICED? But once you get used to it, it’s quite fun, and it frees up the writers to produce some really splendid one-liners. They hit you in the face like a custard pie, but it is terrifically enjoyable: “I always hear ‘Hit me’ when you talk, but usually that’s not what you’re saying’” – “Do you think you could survive for just a few minutes without showing off?” – “I don’t have friends. I just have one.” You have to sit through stuff like “Alone is what I have. Alone protects me.”, “Nope. Friends protect you”, but you get Martin Freeman producing a line like “Would you…just for me? Stop this. Just stop it.” and making it work.

Listening to the show also lets you hear what it’s anxious about. To cite my better-informed friend again, Sherlock has been worrying away at the idea of gaslighting[1] recently. The Hounds of Baskerville played with the idea of not being able to trust your own senses – and even briefly toyed with the fear that someone you love is deliberately doing this to you. The Reichenbach Fall took a similar idea in a different direction: how far can you trust what you think you know about people? And, from Sherlock’s point of view, how hard can you cling to what you know is true, to your sense of who you are, when everyone is saying you’re someone else? By the time the final face-off happens, with its superhero aesthetic of chins and lapels jutting upwards off tall buildings, the emotional ground has already been covered. Moriaty’s crime lies in what he had to do to get Sherlock alone with him against the skyline – this business with snipers and failsafe codes is a bit of a distraction.